CUTANEOUS CYTOLOGY

When do I do it?

When bacterial or yeast infection is suspected (inflammatory alopecia, seborrhea, scales, papule, pustule, crust, erosions, ulcer)
In patients with nodule/tumors- do cytology on every nodule/tumor
In patients with suspected pemphigoid diseases (erosions, pustule, crust)
In every patient with otitis externa

What can I find?

Cocci (most likely Staphylococcus sp.)
Rods → culture and susceptibility advisable
Inflammatory cells with intracellular bacteria → clinically relevant infection that may require systemic antibiotic treatment
Eosinophils → can point to ectoparasites or allergies
Macrophages → seen in chronic, sterile and infectious processes
Malassezia spp. → one or more Malassezia sp. per oil immersion field (x 1000 magnification) may be clinically relevant (normal numbers vary can vary with the climate.) In cases of Malassezia hypersensitivity a much lower number of Malassezia (e.g. one in every two or three HPFs) can cause clinical disease. Topical or systemic treatment should be considered.
Neoplastic cells

TECHNIQUE IMAGES : CUTANEOUS CYTOLOGY

Superficial pyoderma (Courtesy of Sonya Bettenay)

Use the adhesive tape technique on dry skin or in the interdigital area (Courtesy of Sonya Bettenay)

Impression smear: slide pressed on skin (Courtesy of Sonya Bettenay)

Aspiration smear: insert needle into nodule (Courtesy of Sonya Bettenay)

Micrograph showing eosinophils, neutrophils and bacteria

Eosinophils, neutrophils and bacteria (Courtesy of Sonya Bettenay)

Superficial pyoderma: neutrophils with intracellular cocci (Courtesy of Sonya Bettenay)

Micrograph showing pyogranulomatous inflammation

Pyogranulomatous inflammation (deep pyoderma): many neutrophils and macrophages, few bacteria (Courtesy of Stefanie Peters)

Micrograph showing malassezia and bacteria

Malassezia and bacteria (Courtesy of Stefanie Peters)

Grade 1 mast cell tumor with eosinophils (Courtesy of Sonya Bettenay)

What do I need?

Slides, DiffQuick® or similar stain, mineral oil, adhesive tape, microscope, needle and syringe

How do I do it?

Impression smear

Rub or impress a slide on moist, exuding or greasy surface of infected skin.
Role a cotton bud on the skin surface or insert it in the ears and role cotton bud on the slide.
Insert needle (25 - 27 ga.) into the pustule holding the needle parallel to the skin so that only the pustule is punctured, no deeper cells or blood are required, top is lifted off and slide impressed onto the ruptured pustule.
Use the sticky surface of the adhesive tape to collect cells and surface organisms from dry and / or scaly skin and then place this (sticky side down) onto a glass slide with a drop of the blue Difff-Quick^® stain. The tape acts as its own coverslip.
Apply a piece of double-sided adhesive tape to a slide and collect material with the sticky slide. Stain this in the blue Diff-Quick^® stain, dry and examine under oil immersion.

Aspiration smear

Insert needle into nodule or abscesses and re-insert a number of times without leaving the skin. Withdraw the needle. A syringe with the plunger pulled back is attached to the needle and contents is blown onto a slide and air dried.
Stain the air dried slides (e.g. Diff-Quick^®)
Put the slides under a microscope, condenser up.

Tip

In case of dry skin or in the interdigital area:

Moisten a cotton bud with saline solution or carefully rub the edge of a slide on the skin and then rub the material on the slide
Press clear adhesive tape (sticky side down) onto the skin. Stain the tape like a slide, let it air dry and press it onto a slide or put a drop of the blue stain o DiffQuick^® on a slide and press the tape sticky side down on the drop. Evaluate under a microscope.

abscess

A discrete swelling containing purulent material, typically in the subcutis

Perianal abscess in a dog

alopecia

Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma

Extensive alopecia secondary to cutaneous epitheliotropic lymphoma

alopecia (“moth-eaten”)

well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis

“Moth-eaten” alopecia secondary to superficial bacterial folliculitis

angioedema

Regional subcutaneous edema

Angioedema due to cutaneous drug eruption

annular

Ring-like arrangement of lesions

Annular lesions in a dog with erythema multiforme

atrophy

Thinning of the skin or other tissues

Cutaneous atrophy due to glucocorticoids

bulla

Fluid-filled elevation of epidermis, >1cm

Bullae in a dog with bullous pemphigoid

hemorrhagic bullae

Blood-filled elevation of epidermis, >1cm

Interdigital hemorrhagic bulla in a dog with deep pyoderma and furunculosis

comedo

dilated hair follicle filled with keratin, sebum

Comedones on the ventral abdomen of a dog with hypercortisolism

crust

Dried exudate and keratinous debris on skin surface

Multifocal crusts due to pemphigus foliaceus

cyst

Nodule that is epithelial-lined and contains fluid or solid material.

Epidermal inclusion cyst

depigmentation

Extensive loss of pigment

Depigmentation of planum nasale in dog with vitiligo.

ecchymoses

Patches due to hemorrhage >1cm

Ecchymoses of a dog’s leg due to vasculitis

epidermal collarettes

Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles

Epidermal collarettes in a dog with Staphylococcus superficial bacterial folliculitis

erosion

Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.

Erosions in a dog with vasculitis

erythema

Red appearance of skin due to inflammation, capillary congestion

Erythema in a dog with cutaneous drug eruption

eschar

Thick crust often related to necrosis, trauma, or thermal/chemical burn

Eschar from physical trauma

excoriation

Erosions and/or ulcerations due to self-trauma

Excoriations in a cat with atopic dermatitis

fissure

Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.

Fissures of the footpads in a dog with superficial necrolytic dermatitis

fistula

Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues

Perianal fistulas in a dog

follicular casts

Accumulation of scale adherent to hair shaft

Follicular casts surrounding hairs from a dog with hypothyroidism

hyperkeratosis

Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.

Idiopathic hyperkeratosis of the nasal planum (left) and footpads (right)

hyperpigmentation

Increased melanin in skin, often secondary to inflammation

Inflammatory lesions (left) resulting in post-inflammatory hyperpigmentation (right)

hypopigmentation

Partial pigment loss

Idiopathic hypopigmentation of planum nasale

hypotrichosis

Lack of hair due to genetic factors or defects in embryogenesis.

Congenital hypotrichosis in chocolate Labrador puppies.

leukoderma

Lack of cutaneous pigment

Macular leukoderma in a dog

leukotrichia

Loss of hair pigment

Progressive leukotrichia in patient with vitiligo.

lichenification

Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture

Lichenification of skin in a dog with chronic atopic dermatitis and Malassezia dermatitis

macule

Flat lesion associated with color change <1cm

Pigmented macule (left) Erythematous macule (right)

melanosis

Increased melanin in skin, may be secondary to inflammation.

Post inflammatory hyperpigmentation of this dog’s thigh

miliary

Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis

Miliary dermatitis in a flea allergic cat

morbiliform

A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas

Morbiliform eruptions in a dog with a cutaneous drug reaction

nodule

A solid elevation >1cm

Nodules on nose of dog with cutaneous histiocytosis.

onychodystrophy

Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia

Onychodystrophy in dog with chronic allergies

onychogryphosis

Abnormal claw curvature; secondary to nail bed inflammation or trauma

Onychogryphosis in a dog with symmetric lupoid onychodystrophy

onychomadesis

Claw sloughing due to nail bed inflammation or trauma

Onychomadesis in a dog with symmetric lupoid onychodystrophy

onychorrhexis

Claw fragmentation due to nail bed inflammation or trauma

Onychorrhexis in a dog with symmetric lupoid onychodystrophy

onychoschizia

Claw splitting due to nail bed inflammation or trauma

Onychoschizia in a dog with symmetric lupoid onychodystrophy

papule

Solid elevation in skin ≤1cm

Papules on a dog with superficial bacterial folliculitis

papules

Solid elevation in skin ≤1cm

Papules on a dog with superficial bacterial folliculitis

paronychia

Inflammation of the nail fold

Paronychia in a dog with symmetric lupoid onychodystrophy

patch

Flat lesion associated with color change >1cm

Hypopigmented patch (left), erythematous patch (right)

petechiae

Small erythematous or violaceous lesions due to dermal bleeding

Petechiae in a dog with cutaneous vasculitis

phlebectasia

Venous dilation; most commonly associated with hypercortisolism

Phlebectasia and cutaneous atrophy due to hypercortisolism in a dog

plaques

Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration

Plaques in a cat with cutaneous lymphoma

pustule

Raised epidermal infiltration of pus

Pustules on the abdomen of a dog with superficial staphylococcal pyoderma.

reticulated

Net-like arrangement of lesions

Reticulated leukotrichia on the back of a horse

scale

Accumulation of loose fragments of stratum corneum

Loose, large scales due to ichthyosis in a Golden Retriever

scar

Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues

Scarring (right) following the healing of an ulcer (left) in a dog with sterile nodular dermatitis

serpiginous

Undulating, serpentine (snake-like) arrangement of lesions

Serpiginous urticarial lesions on a horse

telangiectasia

Permanent enlargement of vessels resulting in a red or violet lesion (rare)

Telangiectasia in a dog with angiomatosis

ulcer

A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.

Ulcerations of the skin of a dog with vasculitis.

urticaria

Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction

Urticaria in a horse

vesicle

Fluid-filled elevation of epidermis, <1cm

Vesicles and bullae on ear pinna due to bullous pemphigoid

wheal

Steep-walled, circumscribed elevation in the skin due to edema

Wheals associated with intradermal allergy testing in a horse